1. Field of the Invention
This invention relates to vehicular semi-automatic mechanical transmission systems and, in particular, to semi-automatic mechanical transmission systems of the type providing partially automatic implementation of a manually or automatically selected changes or shifting of mechanical transmission gear ratios.
More particularly, the present invention relates a control system and method for sensing and indicating (i) a selection of a shift into neutral and (ii) confirmation that a neutral condition is achieved, especially at low vehicle speeds, for a transmission system having a manually controlled throttle and master clutch and only two speed input signals.
2. Description of the Prior Art
Fully automatic transmission systems, both for heavy-duty vehicles such as heavy-duty trucks, and for automobiles, that sense throttle openings or positions, vehicle speeds, engine speeds, and the like, and automatically shift the vehicle transmission in accordance therewith, are well known in the prior art. Such fully automatic change gear transmission systems include automated transmissions wherein pressurized fluid is utilized to frictionally engage one or more members to other members or to a ground to achieve a selected gear ratio as well as automated mechanical transmissions utilizing electronic and/or pneumatic logic and actuators to engage and disengage mechanical (i.e. positive) clutches to achieve a desired gear ratio. Examples of such transmissions may be seen by reference to U.S. Pat. Nos. 3,961,546; 4,081,065 and 4,361,060, the disclosures of which are hereby incorporated by reference.
Such fully automatic change gear transmissions can be unacceptably expensive, particularly for the largest heavy-duty vehicles which are not typically sold in high volumes. Additionally, those automatic change gear transmissions utilizing pressurized fluid and/or torque converters tend to be relatively inefficient in terms of power dissipated between the input and output shafts thereof.
Semi-automatic transmission systems utilizing electronic control units which sense throttle position, engine, input shaft, output shaft and/or vehicle speed, and utilize automatically controlled fuel throttle devices, gear shifting devices and/or master clutch operating devices to substantially fully automatically implement operator manually selected transmission ratio changes are known in the prior. Examples of such semi-automatic transmission systems may be seen by reference to U.S. Pat. Nos. 4,425,620; 4,631,679 and 4,648,290, the disclosures of which are incorporated herein by reference.
While such semi-automatic mechanical transmission systems are very well received as they are somewhat less expensive than fully automatic transmission systems, allow manual clutch control for low speed operation and/or do not require automatic selection of the operating gear ratio, they may be too expensive for certain applications as a relatively large number of sensors and automatically controllable actuators, such as a master clutch and/or a fuel throttle device actuator, are required to be provided, installed and maintained.
At stopped or very low speed vehicle conditions, especially if the vehicle master clutch is manually disengaged, it is difficult to automatically confirm that a vehicle mechanical transmission is in neutral from only inputs indicative of transmission input shaft speed and output shaft speed as the rotational speed sensors will not generate sufficient data to determine that the input and output shaft speeds are not rotating at a possibly engaged transmission ratio. This is especially true if the transmission system is not equipped with automatically controlled master clutch and/or throttle actuators whereby the system could attempt to cause and sense an independent rotation of the input shaft relative to the outshaft which would confirm a neutral condition.
If the operator of a system having a manually operated master clutch is not made aware that although a shift into neutral is selected, it is not yet confirmed, the operator may undertake an unsafe operation, such as rapidly engaging the clutch, or "popping the clutch", not expecting the vehicle motion which may be caused thereby if the transmission is not in neutral.